Method for determining formaldehyde present in air

ABSTRACT

PCT No. PCT/JP97/04863 Sec. 371 Date Apr. 5, 1998 Sec. 102(e) Date Apr. 5, 1998 PCT Filed Dec. 24, 1997 PCT Pub. No. WO98/30897 PCT Pub. Date Jul. 16, 1998The concentration of formaldehyde in air is measured by the method of the invention. More specifically, the invention relates to a method for analyzing formaldehyde in air by collecting the air and implementing an analysis of the concentration of formaldehyde at the site where such air is found.

TECHNICAL FIELD

The present invention relates to a method for analyzing formaldehyde.More specifically, the invention relates to a method for analyzingformaldehyde in the ambient air by collecting formaldehyde gas andsimply implementing an analysis of concentration thereof.

BACKGROUND ART

In recent years, it has been pointed out that toxic gas having harmfulinfluence on a human body is discharged from various new buildingmaterials employed in dwelling houses and so forth. Formaldehyde gas hasbeen listed as one of such toxic gases. Therefore, demand for collectionof the formaldehyde gas in the ambient air and analysis of formaldehydeconcentration is becoming greater.

The basic principle of the analysis of formaldehyde concentration wellknown in the art is as follows. Formaldehyde (HCHO) and AHMT(4-amino-3-hydrazino-5-mercapto-1,2,4-triazole) react under alkalinecondition to form a product which indicates a red color when oxidized byKIO₄ (potassium periodate). The density of this color development is inproportion to the concentration of the formaldehyde. Therefore, ananalytical curve for performing the analysis of the unknown sample isprepared with respect to the relation between light transmittance(absorbance) in the vicinity of wavelength 550 nm and concentration offormaldehyde. The standard operating procedure is as follows.

1 A given amount of the sample solution into which the formaldehyde isadmixed, is measured by means of a pipette and filled into a glassvessel.

2 A given amount of alkaline reagent is measured by means of a pipetteand added to the glass vessel.

3 A given amount of AHMT reagent is measured by means of a pipette andadded to the glass vessel, and left for about 20 minutes while mixing.

4 A given amount of KIO₄ reagent is measured by means of the pipette andadded to the glass vessel.

5 After transferring to a color comparison tube, the color developmentdensity of the resultant solution is measured by means of a colorimeteror a spectrophotometer.

6 The operations of 1 to 5 are performed by using standard solutions (afew of which have different concentrations) containing a known amount offormaldehyde, respectively to prepare an analytical curve.

7 The formaldehyde concentration contained in the sample solution isderived by comparison with the analytical curve.

In addition, the formaldehyde concentration in the ambient air can beconverted by the following equation,

    Cv=Cl×(A×22.4)/(B×M×Q)

wherein,

Cv: HCHO concentration in the ambient air (ppm)

Cl: HCHO content contained in an aliquot portion of liquid (μg)

A: Collecting liquid amount (ml).

B: Amount of the aliquot portion of liquid (ml)

M: Molecular weight of HCHO

Q: Air suction amount (l)

However, according to the conventional method for analyzing formaldehydeset forth above, since the analyzing operation becomes extremelycomplicated, it is necessary to take the formaldehyde collected in thebuilding site back to a location where an analyzing equipment isorganized and implement the analysis of concentration. Therefore, theresult of the analysis cannot be obtained at the site where the gas iscollected, causing the possibility of delay in judgement and assessment.Meanwhile, the condition of the sample may also be changed bytransportation of the collected sample, by transferring of vessels, andduring storage until analysis implementation, all of which may create asituation in which accurate data cannot be obtained.

Furthermore, since a knowledge in chemistry is required for thecalculation of the concentration, and since close attention becomesnecessary upon handling the chemicals for analysis, analysis cannot beimplemented except by a skilled person in chemical analysis. By this,problems such as long-time requirement and high cost by relying on ananalyzing organization or the like are apt to arise.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a method for analyzingformaldehyde in the ambient air, by which accurate measurement isenabled with simple operation, at low cost, without skill requirement,and within a short period of time in the building site.

A method for analyzing formaldehyde in the ambient air according to thepresent invention, comprises the steps of:

passing a given amount of air to be inspected through a collectingvessel filled with a given amount of 2N--KOH solution;

filling a given amount of AHMT reagent into the collecting vessel andleaving the reagent for a given amount of time;

setting a standard color solution to an absorptiometer for adjusting theindication value thereof to a predetermined value; and

adding a given amount of KIO₄ reagent to the collecting vessel, settingthe collecting vessel to the absorptiometer, and detecting formaldehydeconcentration from the indication value of the absorptiometer.

In this case, it is preferable that the composition of the AHMT reagentmay be AHMT:1%, and HCl:1 mol/liter, and the composition of the KIO₄reagent may be KIO₄ :1% and KOH:0.25N.

A method for analyzing formaldehyde in the ambient air according to thepresent invention comprises the steps of:

passing a given amount of air to be inspected through a collectingvessel filled with a given amount of 2N--NaOH solution;

filling a given amount of AHMT reagent prepared by using HClO₄ into thecollecting vessel and leaving the reagent for a given amount of time;

setting a standard color solution to an absorptiometer for adjusting theindication value thereof to a predetermined value; and

adding a given amount of KIO₄ reagent to the collecting vessel, settingthe collecting vessel to the absorptiometer, and detecting formaldehydeconcentration from the indication value of the absorptiometer.

In this case, it is preferable that the composition of the AHMT reagentmay be AHMT:1% and HClO₄ :4 to 5%, and the composition of the KIO₄reagent is KIO₄ :1% and KOH:0.2 to 0.3N.

The collecting vessel may be filled with 2.0 ml or less of the 2N--KOHsolution or 2N--NaOH solution.

The collecting vessel is to be filled with substantially about 0.5 ml ofthe AHMT reagent and the KIO₄ reagent, whether 2N--KOH solution or2N--NaOH solution is used.

Furthermore, the standard color solution may be a standard coloredliquid prepared by using a red color dye having a color densitycorresponding to a color development density caused upon reaction of aknown amount of formaldehyde with the reagent, whether 2N--KOH solutionor 2N--NaOH solution is used.

A method for analyzing formaldehyde in the ambient air according to thepresent invention comprises the steps of:

passing a given amount of air to be inspected through a collectingvessel filled with collecting liquid prepared by adding a given amountof AHMT solution to a given amount of 2N--KOH solution, or with acollecting liquid prepared by adding a given amount of AHMT solutionprepared by using HClO₄ solution to a given amount of 2N--NaOH solution;

setting a standard color solution to an absorptiometer for adjusting theindication value thereof to a predetermined value; and

setting the collecting vessel to the absorptiometer, and detectingformaldehyde concentration from the indication value of theabsorptiometer.

According to the method for analyzing formaldehyde in the ambient airaccording to the present invention mentioned as set forth above,formaldehyde gas in the ambient air can be efficiently collected by2N--KOH solution or 2N--NaOH solution by passing air being inspectedthrough a collecting vessel filled with 2N--KOH solution or 2N--NaOHsolution.

By the use of AHMT reagent and KIO₄ reagent necessary for analysis, anoptimal reaction condition is obtained with respect to 2N--KOH solutionor 2N--NaOH solution.

Especially, since HClO₄ is used for dissolving the AHMT reagent,corrosion of the injection needle and contamination of the reagent canboth be avoided when employing 2N--NaOH solution. Further, since2N--NaOH is employed as the collecting liquid considering that HClO₄ isused for AHMT reagent, it is possible to prevent the sample solutionfrom causing white turbidity.

The standard colored liquid is prepared corresponding to the colordevelopment density developed upon reaction of a known amount offormaldehyde with a reagent, and it is employed as a standard colorsolution. By adjusting the absorptiometer by using the absorbance of thestandard colored liquid as a standard upon absorbance measurement, itbecomes unnecessary to prepare an analytical curve by actuallyperforming reaction of the known amount of the formaldehyde liquid uponeach analysis.

Since the absorptiometer is adjusted by setting the indication value ofthe standard colored liquid to a predetermined value under a premisethat a given amount of the air passes through the reaction vessel, theindication value of the unknown sample can be directly read as theconcentration of the formaldehyde upon measurement of absorbance.Accordingly, calculation using molecular weight and volume conversioncoefficients as gas and so forth of the formaldehyde becomesunnecessary.

Therefore, when performing the analysis of formaldehyde, no specialdevice is required to obtain the results within a short period and atthe site where the gas is collected. Also, expert knowledge and chemicalcalculation becomes unnecessary. Further, transferring or division ofsampled solution becomes unnecessary, and special measuring equipmentfor chemical analysis, which requires skill in handling, are notnecessary.

On the other hand, in case of using the 2N--KOH solution, the AHMTreagent is prepared to have a composition of AHMT:1%, and HCl:1mol/liter, and the KIO₄ reagent is prepared to have a composition ofKIO₄ :1% and KOH:0.25N, and in case of 2N--NaOH solution, the AHMTreagent is prepared to have a composition of AHMT:1% and HClO₄ :4 to 5%,and the KIO₄ reagent is prepared to have a composition of KIO₄ :1% andKOH:0.2 to 0.3N. Accordingly, the AHMT reagent and KIO₄ reagentnecessary for analysis can be set so that optimal reaction condition isobtained with respect to the 2N--KOH solution or 2N--NaOH solution.

The amount of 2N--KOH solution or 2N--NaOH solution used is small as 2.0ml or less, so that high condensation can be achieved even with smallsuction amount of air to facilitate detection even in low gasconcentration. This is an appropriate concentration for certainlymaintaining the reactivity of the AHMT reagent which is addedafterwards, and thus, it becomes unnecessary to add alkaline reagentswhich were used conventionally.

Furthermore, the collecting vessel is to be filled with substantiallyabout 0.5 ml of the AHMT reagent and the KIO₄ reagent whether 2N--KOHsolution or 2N--NaOH solution is used. Since the amount of both reagentsused at one time is small, analyses can be implemented many times evenwhen the amounts of the reagents carried are small. By setting theadding amount of both reagents to be appropriate at 0.5 ml, thepossibility of deterioration in detection sensitivity can be avoided.This problem was caused because conventionally a solution with lowerconcentration was used, which required about four times of adding amountand which lowered color development because of increase in overallliquid amount. On the other hand, the possibility of increase in readingerror of liquid amount upon measurement using an injector can be avoidedwhen the adding amount of the reagent is extremely reduced.

Furthermore, the standard colored liquid, prepared by using a red colordye corresponding to a color development density upon reaction of aknown amount of formaldehyde with a reagent, is employed as the standardcolor solution. Therefore, since the colorimeter (absorptiometer) isadjusted by using the absorbance of the standard colored liquid as astandard upon absorbance measurement, it becomes unnecessary to preparean analytical curve by actually performing a reaction using a knownamount of the formaldehyde liquid for each analysis. Also, if thestandard colored liquid is prepared by using a red color dye, it ispossible to avoid fading of the color development and also possible toavoid the color of the liquid from gradually turning dilute and unstableaccording to elapsed time.

Furthermore, a method for analyzing formaldehyde in the ambient airaccording to the present invention may comprise the following simplifiedsteps of: passing a given amount of air to be inspected through acollecting vessel filled with a collecting liquid prepared by adding agiven amount of AHMT solution to a given amount of 2N--KOH solution, orotherwise a collecting liquid prepared by adding a given amount of AHMTsolution prepared using HClO₄ to a given amount of 2N--NaOH solution;setting a standard color solution to an absorptiometer for adjustment ofthe indication value to a predetermined value; setting the collectingvessel to the absorptiometer; and detecting formaldehyde concentrationfrom the indication value. By this, it is possible to perform theanalyzing operation very simply.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of one embodiment of a gas collecting systemapplicable to a method for analyzing formaldehyde in the ambient airaccording to the present invention;

FIG. 2 is an explanatory illustration of a switching cock provided inthe gas collecting system shown in FIG. 1;

FIG. 3 is a perspective view showing an assembled condition of the gascollecting system shown in FIG. 1;

FIG. 4 is a characteristic diagram of an analytical curve showing therelationship between the gas concentration and absorbance obtained bythe method for analyzing formaldehyde in the ambient air of the presentinvention;

FIG. 5 is a comparative characteristic diagram of the analytical curvesmeasured on different days by the method for analyzing formaldehyde inthe ambient air of the present invention;

FIG. 6 is a characteristic diagram showing the stability of the colordevelopment of a collecting liquid relative to the elapsed timeaccording to the method for analyzing formaldehyde in the ambient air ofthe present invention; and

FIG. 7 is a circuit diagram of another embodiment of a gas collectingsystem applicable to the method for analyzing formaldehyde in theambient air according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention will be discussedhereinafter in detail with reference to the accompanying drawings.

Firstly, discussion will be given for a gas collecting system to beapplied to a method analyzing the formaldehyde in the ambient airaccording to the present invention. The gas collecting system 10includes:

a portable air pump 12 basically driven by a portable battery forsucking gas in an inspection objective space;

an impinger 14 as a collecting vessel in which a collecting liquid 28for collecting an inspection objective gas from the foregoing gas isfilled;

a tube 24 having one end connected to the impinger 14 and the other endcommunicated with the foregoing inspection objective space, the tube 24serving as an induction flow passage which introduces the foregoing gasinto the impinger 14;

a tube 26 having one end connected to the foregoing impinger 14 and theother end connected to a suction port 12a of the foregoing air pump 12,the tube 26 serving as a suction flow passage which introduces theforegoing gas in the impinger 14 into the air pump 12;

a bag 18 connected to a discharge port 12b of the air pump 12 andaccumulating the foregoing gas discharged from the air pump 12, the bag18 serving as a storage body operating as a volumeter;

a drying agent tube 16 disposed between the bag 18 and the impinger 14and serving as drying means for drying the foregoing gas;

a pressure switch 30 detecting an internal pressure of the foregoing bag18;

a tube 36 as a bypass passage connecting the foregoing bag 18 to theforegoing suction port 12a of the foregoing air pump 12 bypassing theforegoing impinger 14;

a switching cock 34 serving as switching means for switching a flowpassage connecting the foregoing bag 18 to either one of the foregoingdischarge port 12b of the foregoing air pump 12 or the foregoing tube36, and in conjunction therewith, connecting the discharge port 12b ofthe air pump 12 to the ambient air communication passage 38 when the bag18 is connected to the tube 36;

a main receptacle box 40 receiving the foregoing air pump 12 and theforegoing battery therein, and in conjunction therewith, having mountingsurfaces 40a and 40b on the outer surface for mounting the foregoingdrying agent tube 16 and the foregoing impinger 14; and

an auxiliary receptacle box 42 mounted on the main receptacle box 40,receiving the foregoing switching cock 34 and the foregoing pressureswitch 30 therein and having a mounting portion 46 for detachablymounting the foregoing bag 18. The impinger 14 is formed of atransparent material and is used as a color comparison tube, and also asa reaction tube to be filled with reagents reacting with the inspectionobjective gas. The pressure switch 30 detects the internal pressure ofthe bag 18 when the predetermined pressure is reached, and outputs astop signal to the air pump 12. Also, the bag 18 is foldable andexchangeable.

Discussing in detail, the shown embodiment of the gas collecting system10 is a type sucking the ambient air, and includes the portable air pump12 as shown in FIG. 1. By sucking the ambient air in the inspectionobjective space by the air pump 12, the inspection objective gas in theambient air is taken in. The foregoing air pump 12 is portable and isdriven by a portable battery, such as a dry cell or the like. In thesuction port 12a of the air pump 12, the impinger 14 and the dryingagent tube 16, which is also used as a filter, are provided insequential order. Also, in the discharge port 12b of the air pump 12,the bag 18 accumulating the gas discharged from the discharge port 12bis provided. The bag 18 is used as a volumeter measuring the gas amount.On the other hand, on the downstream side of the drying agent tube 16, acheck valve 20 permitting only flow of gas in a direction toward thesuction port 12a of the air pump 12 is provided.

The impinger 14 is formed by a bottomed cylindrical glass tube in atest-tube-like configuration, of which an opening portion on the upperend is closed by an elastic cap 22. The tube 24 for introducing theambient air and the tube 26 connecting the interior of the impinger 14to the suction port 12a are provided in the impinger 14. These tubes 24and 26 are formed by injection-needle-like metallic capillaries. Then,the tubes 24 and 26 formed by metallic capillaries are pierced into theelastic cap 22, and the respective needle-shaped tip end portions 24aand 26a are inserted into the impinger 14. Further, a predeterminedamount of the collecting liquid 28 is filled into the impinger 14. Thetip end portion 24a of the tube 24 is dipped into the collecting liquid28, and in conjunction therewith, the tip end portion 26a of the tube 26is located above the liquid surface of the collecting liquid 28.

The pressure switch 30 is provided between the air pump 12 and the bag18. The pressure within the bag 18 is detected by the pressure switch30. At a point of time in which the bag 18 is filled with air, the airpump 12 is stopped.

On the downstream side of the pressure switch 30, a switching cock 34 isprovided in the discharge tube 32 communicated with the bag 18. Theswitching cock 34 connects the bag 18 to the discharge tube 32 of theair pump 12 when set at normal position shown in FIG. 2(a), and connectsthe bag 18 to the tube 36 bypassing the impinger 14 when set at theswitched position shown in FIG. 2(b). At the switched position of theswitching cock 34, the discharge pipe 32 is communicated with theambient air communication passage 38.

The gas collecting system 10 constructed as set forth above, isassembled into a compact construction as shown in FIG. 3. Namely, theauxiliary receptacle box 42 receiving the switching cock 34, thepressure switch 30 and so forth, is mounted onto the side surface 40a,which is the near side of the main receptacle box 40 receiving the airpump 12 and the dry cell or so forth as the driving source, withoccupying approximately half of the space. A lever 44 of the switchingcock 34 is provided projecting from the side surface 42a, which is thenear side of the auxiliary receptacle box 42. Further, a mountingportion 46 of the bag 18 is provided on the side surface 42b, which islocated on the side. Two drying agent tubes 16 are mounted on the sidesurface 40b, which is the side of the main receptacle box 40. Theimpinger 14 is mounted on a position on the side of the auxiliaryreceptacle box 42 on the side surface 40a, which is the near side of themain receptacle box 40. For example, the gas collecting system 10 isformed in a size having 10 cm in depth, 12 cm in width and 18 cm inheight.

In the shown embodiment of the gas collecting system 10 constructed asset forth above, by driving the air pump 12, the ambient air in themeasuring site is introduced into the impinger 14 through the tube 24,and is bubbled through the collecting liquid 28 in the impinger 14, andthen sucked into the air pump 12 through the drying agent tube 16. Thegas discharged from the air pump 12 is accumulated in the bag 18. Then,by using the bag 18 as the volumeter, the pressure switch 30 is actuatedto stop the air pump 12 and terminate the collecting operation of theinspection objective gas when the bag 18 is full. At this point, theinspection objective gas in the ambient air is admixed with thecollecting liquid 28 of the impinger 14, letting the impinger 14 performinspection by functioning as a reaction vessel and the color comparisontube.

After completion of one cycle of the collecting operation, by settingthe switching cock 34 at the switched position shown in FIG. 2(b), thebag 18 is connected to the suction port 12a of the air pump 12. The gasin the bag 18 is then sucked by the air pump 12 to be dischargedautomatically, making the bag empty for preparation for the nextcollection.

Here, the condensation rate of the gas component of the inspectionobjective gas in the collecting liquid 28 collected by the impinger 14is determined by a ratio between the collecting liquid amount and thesucked ambient air amount. Since the impinger 14 is formed compact,condensation and collection can be done by a small amount (1 to 3 ml) ofcollecting liquid. Therefore, high condensation can be obtained withsmall amount of ambient air suction, and the volume of the bag 18 can beas small as 1 to 5 liters. Further, upon colorimetric analysis describedabove, since the impinger 14 can be used as the reaction vessel andcolor comparison tube as it is, the operation for transferring thecollecting liquid 28 or for sampling a part of the collecting liquid 28for analysis becomes unnecessary, thereby improving the operability inchemical analysis. Here, calorimetric analysis means an analyzing methodperformed by adding a reagent to the solution into which the inspectionobjective gas is collected, developing a particular color by chemicalreaction, measuring light transparency by color density, and determiningconcentration of gas component. Commercial small size glass test tubescan be used for the impinger 14, permitting simple handling at quite alow cost in comparison with the conventional impinger.

The elastic cap 22 is fitted on the impinger 14, and large sizeinjection needle-form metallic capillaries are employed for the tube 24and the tube 26 to be set to the elastic cap 22. These tubes 24 and 26can certainly provide flow passages for the air by simply piercingthrough the elastic cap 22. Since the impinger 14 may be operated in acondition where the elastic cap 22 is maintained in a fit-condition, thecollecting liquid 28 will not spill even if the impinger is erroneouslyturned over. In addition, since the collecting liquid 28 and thereagents for reaction can be filled into the impinger 14 whilemaintaining the elastic cap 22 in the set condition, operability andsecurity can be improved. Since the tube 24 and the tube 26 areconstructed as capillaries, they have small diameters, and the bubblesdischarged from the tip end of the tube 24 into the collecting liquid 28becomes smaller, thereby enhancing the dissolving ability of the gascomponent and thus improving collection efficiency.

Furthermore, upon releasing the tube 24 and the tube 26 after completionof the collecting operation of the inspection objective gas, theinterior pressure of the impinger 14 is slightly lowered, and thecollecting liquid 28 residing within the tube 24 is suck into theimpinger 14. Therefore, washing of the tube 24 and tube 26 becomesunnecessary. Also, contamination by the residual liquid can beprevented. In addition, the tip ends of the tube 24 and the tube 26 areformed as closed needles to facilitate insertion into the elastic cap22. Communication openings for the gas are formed as transverse holes inthe vicinity of the tip end portion 24a and 26a so as to preventplugging by tip of the rubber.

As set forth above, the shown embodiment of the gas collecting system 10has a simple construction, wherein the impinger 14 and the drying agenttube 16 are provided in the suction port 12a of the portable air pump12, and the bag 18 is provided in the exhaust port 12b. Therefore, asshown in FIG. 3, these components can be assembled into a compactconstruction as a whole. Accordingly, the gas collecting system 10assembled as set forth above is portable and is provided with superiortransporting ability. Furthermore, adjustment on assembling thecomponents thereof is not needed, and simple collection of the air atany site is possible. Therefore, handling can be simplified and willrequire no skill, permitting anybody's use. In this case, by mountingthe system on a tripod for cameras or so forth, adjustment of height canbe done easily, and the shown system requires less space. Accordingly,the gas collecting system 10 is quite simple in construction and isinexpensive and compact.

Furthermore, the method for analyzing formaldehyde in the ambient airaccording to the present invention is to perform sampling of the air ofthe building site and to measure the concentration of formaldehyde byemploying the gas collecting system 10, as shown in FIGS. 1 to 3, sothat formaldehyde can be easily analyzed from the gas collected by thegas collecting system 10. In the analyzing method according to thepresent invention, the members, such as the impingers 14 which areexchangeable consumable articles, and chemicals can be supplied as ananalysis kit.

The analysis kit to be used when implementing the first embodiment ofthe method for analyzing formaldehyde in the ambient air according tothe present invention is to be provided with:

(i) ten to twenty impingers 14 respectively filled with 2.0 ml ofcollecting liquid 28, wherein 2N--KOH solution (aqueous sodium hydroxideof 2 normals) is employed as the collecting liquid 28;

(ii) one Vial bottle A (having a volume of 50 to 100 ml) containing AHMTreagent;

(iii) one vial bottle B (having a volume of 50 to 100 ml) containingKIO₄ reagent;

(iv) several plastic injectors (having a volume of 1 ml);

(v) one impinger containing a standard color solution;

(vi) one sand glass (for 20 minutes use); and

(vii) one portable absorptiometer.

Next, discussion will be made about the operating procedure formeasurement of the concentration of formaldehyde by employing theforegoing analysis kit.

(I) First, the impinger 14 is mounted on the gas collecting system 10 tosuck the gas containing formaldehyde. At this time, the standard gassuction amount is 3 liters, and the standard required time is estimatedas 10 minutes.

(II) 0.5 ml of AHMT reagent is taken from the vial bottle A by theinjector and added to the impinger 14. The impinger is left in thiscondition for 15 to 20 minutes or longer. At this time, the sand glassis used.

(III) While adding AHMT reagent to the impinger 14 and leaving the same,the standard color solution is set to the absorptiometer. Then, a dialis adjusted so that the indication value comes to a predetermined value.

(IV) 0.5 ml of KIO₄ reagent is taken from the vial bottle B by theinjector and added to the impinger 14.

(V) The impinger 14 is set to the absorptiometer so that the indicationvalue is read, and the read value is obtained as the concentration offormaldehyde.

Accordingly, in the analysis method of formaldehyde according to thefirst embodiment, the impinger 14 (i) used in the analysis kit canefficiently collect formaldehyde in the gas and enhances the collectionefficiency, since 2N--KOH solution is used. In addition, since theamount of collecting liquid 28 used is small as 2.0 ml, highcondensation can be achieved even with small suction amount of the gas,which facilitates detection even in low gas concentration. This is anappropriate concentration for certainly maintaining the reaction abilityof the AHMT reagent (ii) added afterwards, and thus, it becomesunnecessary to add alkaline reagents.

On the other hand, the concentrations of the AHMT reagent and the KIO₄reagent necessary for analysis are set so that an optimal reactioncondition is obtained with respect to the collecting liquid 28 and sothat the liquid amount being added by the injector can be small. Namely,the AHMT reagent is prepared to have a composition of AHMT:1%, and HCl:1mol/liter, and the KIO₄ reagent is prepared to have a composition ofKIO₄ :1% and KOH:0.25N.

The adding amount of both regents are set to be appropriate at 0.5 ml.This is because lower concentration conventionally used required aboutfour times of adding amount, which lowered sensitivity of detection andthe color development since the overall liquid amount increased. On theother hand, when adding amount of the reagent is extremely reduced, thereading error upon measuring of the liquid amount by the injectorbecomes large. In the shown embodiment, since the amount of both reagentused at one time is small as 0.5 ml, analyses can be implemented manytimes even when the amount of the reagents carried are small.

Further, both reagents are contained in the vial bottles A and B of (ii)and (iii), and made into kits. Since these vial bottles are bottles withrubber caps used for injectors, the reagents can be measured and takenby the injector without removing of the caps. Therefore, the reagentwill not spill or be deposited onto the hand.

Next, the standard color solution described in (v) is preliminarilyprepared in a laboratory by taking a standard colored liquidcorresponding to a color development density developed upon reaction ofa known amount of formaldehyde with the reagent, and is enclosed in thesame container as the impinger 14.

By enclosing the standard color solution in the impinger 14, and byadjusting the colorimeter (absorptiometer) with taking the absorbance ofthe standard colored liquid as a standard upon absorbance measurement,it becomes unnecessary to prepare an analytical curve by actuallyperforming reaction of a known amount of the formaldehyde liquid foreach analysis. Also, since the color development density of the coloredliquid developed by reacting formaldehyde becomes unstable and the colorgradually turns dilute according to elapsed time, the standard coloredliquid is prepared by using a red color dye having less fading.

On the other hand, since the color collecting system 10 has aconstruction which can constantly suck a predetermined amount of gas, byadjusting the indication value of the absorptiometer to a predeterminedvalue by using the standard colored liquid under a premise of thesuction gas amount, the indication value of the unknown sample can bedirectly read as the concentration of the formaldehyde upon measurementof absorbance. Accordingly, calculation using molecular weight offormaldehyde and volume conversion coefficients as gas or so forthbecomes unnecessary. Also, as for the portable absorptiometer of (vii),a compact and lightweight one operated by a dry cell is used, and it hasa perimselective filter of wavelength 530 nm.

Accordingly, in the shown embodiment, since formaldehyde concentrationis measured by sucking the gas by the gas collecting system 10 byemploying the impinger 14, the AHMT reagent, KIO₄ reagent, the injector,the standard color solution, the sand glass and the portableabsorptiometer forming the kit, the system can be made compact to beeasily handled and requires no special device. Thus, a result can beobtained within a short period of time at the site where the gas iscollected. On the other hand, expert knowledge and chemical calculationbecomes unnecessary, and also, transferring or division of the sampledsolution becomes unnecessary. Therefore, there is no need for specialmeasuring equipment (such as transfer pipettes or the like) for chemicalanalysis, which require skill in handling.

The collecting liquid 28 and the reagents can be taken by the injectorwithout releasing the cap. Therefore, even if the bottle is turned over,the content will never be spilled, thereby permitting safe operation. Inaddition, since analysis can be performed at the gas sampling site, itbecomes unnecessary to pay any attention for transportation of thesample. Also, it becomes unnecessary to rely on an outer analyzingorganization requiring high cost. Since result can be obtainedimmediately at low cost, measurements can be performed many timessequentially along with observation of the results.

As set forth above, in the shown embodiment of the formaldehydeanalyzing method, no expert knowledge is required in measurement ofconcentration of formaldehyde, and this permits simple and easyoperation at low cost and within a short period of time. Therefore, evenwhen inspection is performed within a new building, a large amount ofinspection data, such as amount of formaldehyde generated from variousconstruction materials, and amount of formaldehyde present in the roomenvironment, can be obtained.

In the shown embodiment, it is possible to simply measure theformaldehyde concentration, and also obtain the equal results comparedwith the conventional analyzing method as shown in Table 1 below.Namely, Table 1 is prepared by measuring formaldehyde concentration ofindoor air within an actual dwelling unit. As a comparative prior art,the results of an analysis by means of high performance liquidchromatograph well known as a high-level analyzing method is shown.

                  TABLE 1                                                         ______________________________________                                                 Result of actual measurement of                                        formaldehyde concentration                                                    in an indoor air                                                            Data       Method of the                                                                             Precise method in                                        No. present invention the prior art                                         ______________________________________                                        1          0.220 ppm   0.23 ppm                                                 2 0.190 ppm 0.19 ppm                                                          3 0.128 ppm 0.14 ppm                                                          4 0.115 ppm 0.12 ppm                                                        ______________________________________                                    

In the table above, four data (No. 1 to 4) are indicated, each of whichhaving a condition different from each other in the inspection dwellingunit and the inspection time zone. In the method of the shownembodiment, the gas collecting system 10 is employed to suck 3 liters ofthe air for about 10 minutes, and the data analyzed in the building siteusing an analysis kit is applied. On the other hand, in the conventionalmethod, a commercial DNPH cartridge for collecting the formaldehyde isemployed to suck 25 to 30 liter of the air for about 30 minutes, and thecartridge is transported by means of a cold storage vessel to ananalyzing organization. The data obtained by means of HPLC (highperformance liquid chromatograph) after solvent-extraction are listed.

FIG. 4 is an illustration of one example of an analytical curve showingthe relation between formaldehyde concentration and absorbance byemploying the analysis kit of the shown embodiment. The vertical axis(y) represents the color density of the reaction product of theformaldehyde shown as the absorbance at 530 nm wavelength, and thetransverse axis (x) represents the theoretical formaldehydeconcentration (volume ppm) in case of taking 3 liters of air suction andby using a concentration-known formaldehyde liquid. The graph showsthese correlation. By this graph, the following regression equation canbe derived.

    x=0.5525y+0.00138

Therefore, it can be understood that a linear relationship isestablished between the gas concentration and absorbance, and thus theshown embodiment has the performability to sufficiently detect theformaldehyde concentration in practical range.

FIG. 5 is an illustration of one example of a comparison of theanalytical curve being measured twice on different testing days (blackcircle indicates the one measured later). From FIG. 5, it can beunderstood that the repeatability of the measured value is excellent.The meanings of the vertical axis and the transverse axis of the graphare the same as those of the graph of FIG. 2.

Furthermore, FIG. 6 is an illustration showing a data example forconfirming the stability of the color development liquid afterdeveloping of color. From FIG. 6, it can be understood that it isunnecessary to measure the absorbance (concentration) immediately afterdeveloping the color, but the measurement after a long time elapsed isundesirable. Therefore, the standard color solution included in theanalysis kit is to be prepared using a stable dye. Here, the verticalaxis presents the color density of the reaction product of theformaldehyde shown as the absorbance at 530 nm wavelength, and thetransverse axis represents the elapsed number of days. Furthermore,formaldehyde concentration is indicated in μg/ml.

In the second embodiment of the formaldehyde analyzing method, theanalysis kit is provided with:

(i) ten to twenty impingers 14 respectively filled with 2.0 ml of2N--NaOH solution (aqueous sodium hydroxide of 2 normals) employed asthe collecting liquid 28;

(ii) one vial bottle A (having a volume of 50 to 100 ml) containing AHMTreagent prepared using HClO₄ ;

(iii) one vial bottle B (having a volume of 50 to 100 ml) containingKIO₄ reagent;

(iv) several plastic injectors (having a volume of 1 ml);

(v) one impinger containing a standard color solution;

(vi) one sand glass (for 20 minutes use); and

(vii) one portable absorptiometer.

On the other hand, the concentrations of the AHMT reagent and the KIO₄reagent necessary for analysis are set so that an optimal reactioncondition is obtained with respect to the collecting liquid 28, and sothat the liquid amount to be added by the injector can be small. Namely,the AHMT reagent is prepared to have a composition of AHMT:1%, and HClO₄:4 to 5%, and the KIO₄ reagent is prepared to have a composition of KIO₄:1% and KOH:0.2 to 0.3 N.

The operation procedure for measuring formaldehyde concentration bymeans of the foregoing analysis kit is the same as that of the firstembodiment.

On the other hand, in the second embodiment, the following matters areconsidered in regard of the collecting liquid 28 and the AHMT reagent.Since AHMT reagent cannot be dissolved without adding acid, it isnormally dissolved by adding HCl. The reagent is sampled by the injectoras set forth above in order to improve operability upon handling.However, by repeatingly sampling the HCl-added AHMT reagent with theinjector, corrosion of the injection needle may be caused by the effectof HCl. Thus, the life of the needle is considered to be quite short.Also, the reagent may be contaminated by eluted substance from theneedle, such as iron ion produced by corrosion of the needle, which maypossibly cause error in analysis. Therefore, in the shown secondembodiment, HClO₄ is used in place of HCl for dissolving AHMT reagent.In this way, corrosion of the injection needle and contamination of thereagent can be avoided. On the other hand, in addition to the foregoing2N--NaOH, 2N--KOH (potassium hydroxide solution of 2 normals) may beemployed as the collecting liquid 28. However, when HClO₄ is employed inthe AHMT reagent, and at the same time 2N--KOH is employed as thecollecting liquid 28, HClO₄ and KOH react to produce potassiumperchlorate at the time when the AHMT reagent is added to the collectingliquid 28. Potassium perchlorate is difficult to be dissolved in water,and causes white turbidity of the sample solution. Therefore,considering that HClO₄ is used for the AHMT reagent, 2N--NaOH isemployed as the collecting liquid 28.

In either analyzing method of the first or second embodiments, AHMTreagent is added to the collecting liquid 28 after the gas collectingoperation, and subsequently, KIO₄ reagent is added. Here, an embodimentof an analyzing method for formaldehyde which can further simplify theanalyzing method will be discussed.

In this case, the analysis kit is provided with:

(i) ten to twenty impingers 14 normally filled with 2 to 3 ml of thecollecting liquid 28 which is a 2N--KOH solution or a 2N--NaOH solution;

(ii) one impinger containing the standard color solution;

(iii) several plastic injectors (having volume of 1 ml); and

(iv) one portable absorptiometer.

Particularly, the shown embodiment is designed to eliminate theoperation for adding the reagent after completion of collection and thewaiting time for the reaction process, by causing the color developmentreaction while collecting the formaldehyde gas. Therefore, in the shownembodiment, the collecting liquid 28 is prepared by mixing an alkalinereagent and a reducing reagent, such as sodium hyposulfite and so forth,at an appropriate mixing ratio.

In the conventional method, three kinds of reagents, the alkalinereagent, the AHMT reagent, and KIO₄ reagent, are used separately. In thecase where these reagents are preliminarily mixed, normal reaction withformaldehyde cannot be caused. Therefore, it becomes necessary to addthem separately in a predetermined sequential order and by keeping timeinterval required for reaction.

In contrast to this, when the collecting agent 28 of the shownembodiment is employed, it becomes possible to add AHMT liquid to thecollecting liquid 28 before gas collecting operation, and the KIO₄reagent becomes unnecessary.

Then, since AHMT reagent can be added in advance, color developmentreaction can be caused along with the gas collection, and the gascollecting operation can be performed while visually monitoring thecondition thereof. Since color development reaction is progressed alongwith the gas collection, it becomes possible to omit the waiting periodfor the reaction caused by adding the AHMT reagent after gas collection.Furthermore, although KIO₄ reagent is required to generate a red coloredsubstance by oxidizing the reaction intermediate product of AHMT reagentand formaldehyde, since AHMT reagent can be added in advance, the oxygenin air introduced into the collecting liquid 28 during the process ofgas collection serves as an oxidation agent and functions as areplacement for KIO₄ reagent. Therefore, KIO₄ reagent becomesunnecessary.

Next, the operation procedure in measurement of formaldehydeconcentration using the analysis kit will be discussed hereinafter.

In this case, the procedure is quite simple.

(I) 0.5 ml of AHMT solution is added by the injector to the impinger 14containing the collecting liquid 28, then gas is sucked. At this time,the standard gas suction amount is 3 liters, and the standard requiredtime is 10 minutes.

(II) The impinger 14 is set to the absorptiometer, and the indicationvalue is read, and the read value is obtained as the formaldehydeconcentration.

Namely, in the shown embodiment, a given amount of collecting liquid 28,which is prepared by mixing the alkaline reagent and the reducingreagent such as sodium hyposulfite and so forth at an appropriate mixingratio, is filled in the impinger 14. Then, the given amount of the gasin the inspection objective space is passed through the impinger 14. Inconjunction therewith, the standard color solution is set to theabsorptiometer for adjusting the indication value to a predeterminedvalue. Then, the impinger 14 is set to the absorptiometer, and ananalysis is made by detecting formaldehyde concentration from theindication value.

Not to mention, in the preferred embodiment set forth above, it is alsopossible to obtain the same operation and effect as those of theforegoing first and second embodiments.

FIG. 7 is an illustration of another embodiment of the gas collectingsystem 10c which is applicable to the method for analyzing formaldehydein the ambient air according to the present invention. The gascollecting system 10c is a type in which the inspection objective gas iscollected while the gas in the inspection objective space enclosed by acasing 96 is circulated within a closed loop circuit.

The gas collecting system 10c has a casing 118 formed into ahemisphere-shape with a transparent material having a given thicknessfor collecting the inspection objective gas naturally discharged fromthe inspecting portion. Around the casing 118, an impinger 128, an airpump 124, a humidity conditioner bottle 136 and a buffer 134 areconnected in sequential order to form a closed flow passage forcirculating the gas so that the gas in the casing 118 is forcedly suckedby the air pump 124 and is circulated to collect the inspectionobjective gas with the impinger 128.

In the casing 118, a gas circulating port 122 for taking in thecirculating gas, and a gas circulating port 120 feeding the gas mixedwith the inspection objective gas from the casing 118, are provided inopposed position. A packing 138 formed of soft rubber or the like ismounted on the peripheral edge of the opening 118a of the casing 118.The packing 138 is abut onto the surface of the inspection object 80 tosealingly enclose the interior of the casing 118.

The impinger 128 filled with the collecting liquid 126, the tube 130introducing gas thereinto, and the tube 132 thus feeding out the gas aresimilar to the impinger 14, the tubes 24 and 26 described in the firstembodiment.

The air pump 124 is portable and driven by a battery, such as a dry cellor the like, similar to the first embodiment. The suction port 124a isconnected to the impinger 128 via the tube 132, and the discharge port124b is connected to a humidity conditioner bottle 136.

The humidity conditioner bottle 136 is formed by a cylindrical glassbottle. The upper end opening portion is closed by a rubber cap. Apredetermined amount of a humidity conditioner 140, which is of a salinesolution, is filled in the humidity conditioner bottle 136. The tip endof a tube 144 provided on the side introducing the gas is extended intothe liquid of the humidity conditioner 140. The tip end of a tube 146provided on the side discharging the gas is extended above the liquidsurface of the humidity conditioner 140, thereby causing bubbling of theintroduced gas. The tube 144 is connected to the discharge port 124b ofthe air pump 124, and the tube 146 is connected to an induction opening148 of the buffer 134 to maintain the humidity of the gas circulated tothe casing 118. Namely, as the humidity conditioner 140, a saturatedsolution of BaCl₂.2H₂ O can be used as the saline solution. By passingair through the saturated solution, air containing 88% of humidity isobtained at 24.5° C., and the humidity of the passing air is maintainedat the predetermined value. This is because the humidity of the air incontact with the saline solution indicates a constant value, accordingto the kind and concentration of the salt and temperature, in relationto the vapor pressure of the saline solution. Since the values of therelationship with respect to various salts are disclosed in chemicalhandbooks or the like, the salts may be appropriately selected dependingupon the desired humidity.

The buffer 134 is formed with a plastic film or the like and is shapedlike a bag variable of volume. In the buffer 134, an induction opening148 introducing a flowing gas, and a discharge opening 150 feeding outthe interior gas are provided in opposed position. The induction opening148 is connected to the tube 146 coming from the humidity conditionerbottle 136, and in conjunction therewith, the discharge opening 150 isconnected to the gas circulating portion 122 of the casing 118 so thatit may be expand and vary the volume of the buffer depending upon thedifference between the gas pressure introduced thereinto and the ambientair pressure. Namely, when the internal pressure is elevated, the bufferis expanded, and when the internal pressure is reduced, the buffer iscontracted, making the pressure difference between the inside and theoutside to naturally be zero, and this enables circulation withoutcausing variation in pressure of the gas.

Then, in this gas collecting system 10c, the opening 118a of the casing118 is abut onto the inspection object 80, and in conjunction therewith,the air pump 124 is driven. At this time, since the packing 138 isprovided on the opening 118a of the casing 118, the abutted portion issealingly enclosed by abutting the packing 138 onto the surface of theinspection object 80. Further, since the casing 118 is formedtransparent, the setting condition can be checked, and the condition ofthe surface of the inspection object 80 can be easily observed. Sincethe gas is sucked by the air pump 124, the gas within the casing 118 isintroduced into the impinger 128, and is bubbled through the collectingliquid 126 in the impinger 128 to be sucked into the air pump 124. Thesucked gas is discharged from the discharge portion 124b of the air pump124 to be returned to the interior of the casing 118 through thehumidity conditioner bottle 136 and the buffer 134 for circulation. Atthis time, the inspection objective gas from the inspection object 80 isdischarged from the inside of the enclosed casing 118, and is capturedin the collecting liquid 126 by bubbling through the collecting liquid126 of the impinger 128. Then, the gas returned within the casing 118from the buffer 134 is purified since the inspection objective gas iscaptured by the impinger 128. Also,the humidity thereof is maintainedconstant by the humidity conditioner bottle 136.

Thus, collection of the inspection objective gas is performed for apredetermined period of time by circulating the gas and by collectingthe inspection objective gas, whereby an analysis is performed by achemical method to determine the amount of the inspection objective gascontained in the collecting liquid 126 of the impinger 128. At thistime, the amount of gas discharged can be derived by the followingequation (1).

    discharge amount of inspection objective gas=collected gas amount/(opening area of casing×period of collecting operation)      (1)

The shown embodiment of the gas collecting system 10c can performinspection for construction materials alone, and as well, can collectthe inspection objective gas of the material already in use, namely, ofany portion of a building after construction is completed.

As set forth above, according to the method for analyzing formaldehydein the ambient air of the present invention, the formaldehyde gas can beefficiently collected by the collecting liquid, by passing the gas to beinspected through the collecting vessel filled with 2N--KOH solution or2N--NaOH solution as the collecting liquid.

Since the analysis is implemented by using AHMT reagent and KIO₄reagent, the optimal reaction condition can be obtained with respect to2N--KOH solution or 2N--NaOH solution, and therefore the accuracy ofanalysis can be enhanced.

Further, by using 2N--NaOH solution as the collecting liquid, and usingHClO₄ for dissolving the AHMT reagent, corrosion of the injection needlecan be avoided and contamination of the reagent can be prevented.Moreover, since 2N--NaOH is used as the collecting liquid consideringthat HClO₄ is also used for AHMT reagent, it is possible to avoidcausing white turbidity of the sample solution.

Furthermore, the standard colored liquid, which corresponds to a colordevelopment density upon reaction of a known amount of formaldehyde witha reagent, is prepared as the standard color solution, and theabsorptiometer is adjusted by taking the absorbance of this standardcolored liquid as a standard upon absorbance measurement. Therefore, thecomplicated operation for preparing an analytical curve by actuallyperforming reaction of a known amount of the formaldehyde liquid peranalysis becomes unnecessary.

Furthermore, by adjusting the absorptiometer to a predetermined value bythe use of the standard colored liquid under a premise that a givenamount of air passes through the reaction vessel, the indication valueof the unknown sample can be directly read as the concentration of theformaldehyde upon measurement of absorbance. Accordingly, calculationusing molecular weight of formaldehyde and volume conversioncoefficients as gas or so forth becomes unnecessary, and expertknowledge and chemical calculation becomes unnecessary. Also,transferring or division of the sampled solution becomes unnecessary,therefore requiring no skill in handling.

Therefore, according to the analyzing method of the present invention,an accurate result can be obtained within a short period of time at thesite where the gas is collected.

What is claimed is:
 1. A method for analyzing a concentration offormaldehyde in air, comprising:passing a given amount of said airthrough a collecting vessel comprising a given amount of an alkalinesolution, said collecting vessel being filled with said given amount ofsaid alkaline solution before passing said given amount of said air;filling a given amount of an AHMT reagent into said collecting vesseland leaving said reagent in said collecting vessel for a given period oftime; using a standard color solution for calibrating an indicationvalue of an absorptiometer to a predetermined value; adding a givenamount of KIO₄ to said collecting vessel; and setting said collectingvessel in said absorptiometer to detect said formaldehyde concentrationfrom a value of the indication value of said absorptiometer,wherein saidconcentration of formaldehyde is directly indicated by the value of theindication value of said absorptiometer.
 2. The method for analyzing theformaldehyde concentration in air as set forth in claim 1, wherein saidalkaline solution is a 2N--KOH solution and said collecting vessel isfilled with 2.0 ml or less of said 2N--KOH solution.
 3. The method foranalyzing the formaldehyde concentration in air as set forth in claim 1,wherein said collecting vessel is filled with substantially about 0.5 mlof said AHMT reagent and said KIO₄ reagent.
 4. The method for analyzingthe formaldehyde concentration in air as set forth in claim 1, wherein acomposition of said AHMT reagent is AHMT:1%, and HCl:1 mol/liter, and acomposition of said KIO₄ reagent is KIO₄ :1% and KOH:0.25N.
 5. Themethod for analyzing the formaldehyde concentration in air as set forthin claim 1, wherein said standard color solution is a standard coloredliquid prepared by using a red color dye corresponding to a colordevelopment density developed upon reaction of a known amount offormaldehyde with a reagent.
 6. The method for analyzing theformaldehyde concentration in air as set forth in claim 1, wherein saidalkaline solution is a KOH solution.
 7. The method for analyzing theformaldehyde concentration in air as set forth in claim 1, wherein saidalkaline solution is a 2N--KOH solution.
 8. A method for analyzing aconcentration of formaldehyde in air, comprising:passing a given amountof said air through a collecting vessel comprising a collecting liquidprepared by adding a given amount of an AHMT solution to a given amountof an alkaline solution; using a standard color solution for calibratingan indication value of an absorptiometer to a predetermined value;setting said collecting vessel in said absorptiometer, and detectingsaid formaldehyde concentration from a value of the indication value ofsaid absorptiometer,wherein said concentration of formaldehyde isdirectly indicated by the value of the indication value of saidabsorptiometer.
 9. The method for analyzing the formaldehydeconcentration in air as set forth in claim 8, wherein said alkalinesolution is a KOH solution.
 10. A method for analyzing a concentrationof formaldehyde in air, comprising:passing a given amount of said airthrough a collecting vessel comprising a given amount of an alkalinesolution, said collecting vessel being filled with said given amount ofsaid alkaline solution before passing said given amount of said air;filling a given amount of an AHMT reagent prepared by using HClO₄ intosaid collecting vessel and leaving said reagent in said collectingvessel for a given period of time; using a standard color solution forcalibrating an indication value of an absorptiometer to a predeterminedvalue; adding a given amount of KIO₄ to said collecting vessel; andsetting said collecting vessel in said absorptiometer to detect saidformaldehyde concentration from a value of the indication value of saidabsorptiometer,wherein said concentration of formaldehyde is directlyindicated by the value of the indication value of said absorptiometer.11. The method for analyzing the formaldehyde concentration in air asset forth in claim 10, wherein said alkaline solution is a 2N--NaOHsolution and said collecting vessel is filled with 2.0 ml or less ofsaid 2N--NaOH solution.
 12. The method for analyzing the formaldehydeconcentration in air as set forth in claim 10, wherein said collectingvessel is filled with substantially about 0.5 ml of said AHMT reagentand said KIO₄ reagent.
 13. The method for analyzing the formaldehydeconcentration in air as set forth in claim 10, wherein a composition ofsaid AHMT reagent is AHMT:1% and HClO₄ :4 to 5%, and a composition ofsaid KIO₄ reagent is KIO₄ :1% and KOH:0.2 to 0.3N.
 14. The method foranalyzing the formaldehyde concentration in air as set forth in claim10, wherein said standard color solution is a standard colored liquidprepared by using a red color dye corresponding to a color developmentdensity developed upon reaction of a known amount of formaldehyde with areagent.
 15. The method for analyzing the formaldehyde concentration inair as set forth in claim 10, wherein said alkaline solution is a NaOHsolution.
 16. The method for analyzing the formaldehyde concentration inair as set forth in claim 10, wherein said alkaline solution is a2N--NaOH solution.
 17. A method for analyzing a concentration offormaldehyde in air, comprising:passing a given amount of said airthrough a collecting vessel comprising a collecting liquid prepared byadding a given amount of an AHMT solution prepared by using HClO₄ to agiven amount of an alkaline solution; using a standard color solutionfor calibrating an indication value of an absorptiometer to apredetermined value; setting said collecting vessel in saidabsorptiometer, and detecting said formaldehyde concentration from avalue of the indication value of said absorptiometer,wherein saidconcentration of formaldehyde is directly indicated by the value of theindication value of said absorptiometer.
 18. The method for analyzingthe formaldehyde concentration in air as set forth in claim 17, whereinsaid alkaline solution is a NaOH solution.